It is intended to determine the three dimensional structure of a simple virus at atomic resolution using X-ray crystallography. In particular, the study of southern bean mosaic virus (SBMV) has now progressed to a semi-interpretable 4.0 Angstroms resolution electron density map. It is anticipated that a 2.8 Angstroms resolution map will be calculated in 1979. Hopefully, the complete polypeptide backbone of each protein subunit will then be determined and, in addition, possible some of the RNA secondary structure. Work is also in progress on the metal-free, swollen virus, and on crystallization of the component protein subunits. These experiments are directed to an elucidation of the mode of self-assembly of SBMV.